Advanced adsorbent for PSA

ABSTRACT

The invention relates to adsorbent materials having comparatively high intrinsic adsorption rates. Methods are disclosed whereby such rates can be achieved. In preferred embodiments, the adsorbent is a LiX zeolite material.

This application claims the benefit of Provisional Application Ser. No.60/076,344 filed Feb. 27, 1998.

FIELD OF THE INVENTION

The invention relates to pressure swing adsorption processes and moreparticularly to PSA processes for the production of high purity oxygen(e.g. oxygen having a purity of 90-95 vol. % O₂). More particularly, theinvention is directed towards particular adsorbents for use in PSAprocesses.

OBJECTS OF THE INVENTION

The objective of this invention is to enhance the mass transfer rate ofadsorbent materials, particularly those used in PSA. With a fast masstransfer rate, one can have short cycle time and low power consumptionand therefore high adsorbent productivity and high process efficiency inPSA systems and processes.

BACKGROUND OF THE INVENTION

It has been recognized that it is possible to shorten cycle time byreducing particle size of adsorbent aggregates. This recognition hasbeen based upon the assumption that the time needed for adsorbates totravel through the macropores of the adsorbents limits theadsorption/desorption cycle time, i.e. macropore diffusion is the ratelimiting step in adsorption processes.

Armond et al. (UK Pat. Appl. GB 2 091 121) disclose a superatmosphericPSA process for air separation in which short cycles (<45 sec) arecombined with aggregates of small diameter (0.4 mm to 3.0 mm) to reducethe process power and the size of the adsorption bed. They reported thatcycle times of 15 s to 30 s and aggregate diameter of 0.5 mm to 1.2 mmare their preferred choice.

Hirooka et al. (U.S. Pat. No. 5,122,164) also utilized small particlesto achieve fast cycles and they devised process cycles with 6, 8 or 10process steps to improve yield and productivity. They preferredaggregate diameter of 0.8 mm to 1.7 mm and cycle times of 50 s to 60 s.

Very small adsorbent particles (0.1 mm to 0.8 mm) are necessary for thefast cycles and high pressure drop that characterize a special class ofprocesses known as rapid pressure swing adsorption (RPSA). Typical RPSAprocesses have very short feed steps (often less than 1.0 s) operatingat high feed velocities, include a flow suspension step following thefeed step and generally have total cycle times less than 20 s (oftenless than 10 s).

Jones et al teaches that RPSA of single adsorption bed using adsorbentaggregates of 20-120 mesh (0-84mm to 0.125 mm) is able to achieve acycle time of less than 30 seconds (U.S. Pat. No. 4,194,892). Earls etal teach RPSA air separation using multi-bed cycles using 40 to 120 mesh(0.520 mm to 0.125 mm) aggregates and a cycle time from 0.2 to 18seconds (U.S. Pat. No. 4,194,891).

Wankat developed a methodology to scale columns according to particlediameter whereby through the use of smaller diameter, one can reduce thevolume of adsorbents needed. This is referred to as “intensification” ofthe sorption process. (P C Wankat, Ind. Eng. Chem. Res. Vol. 26, No. 8,p.1579 1987).

Unfortunately,. however as the diameter of the aggregates decreases, thepressure drop across the bed increases. Further, there is increasedpotential for fluidization and greater difficulty in particle retentionin the bed. The net effect is an undesirable increase in the energyconsumption of the process.

Kinetics of sorption in PSA processes has been discussed in texts suchas “Principles of Adsorption and Adsorption Processes” by Ruthven, JohnWiley & Son, 1984; and Gas Separation by Adsorption Processes, by Yang,Butterworth, 1987). In these discussions, the kinetic parameter of anadsorbent is defined as a function of the macropore diffusioncoefficient, which in turn has been defined as a function of theporosity of the macropore.

Based on these theoretical developments, Moreau et al (U.S. Pat. No.5,672,195) concluded that an adsorbent should have a kinetic parameterA(k) of at least 0.5 s⁻¹ and a porosity of between 0.38 and 0.6. Moreauet al did not address the significant offsetting effects of highporosity, including the fact that increasing the porosity orintraparticle void fraction reduces the overall active adsorbent contentof the particle resulting in lower particle density. This in turnincreases the volume of adsorbent required for a given N₂ adsorbatecapacity (mol/g). The larger internal void fraction associated withincreased porosity also increases the non-selective gas storage volumein the adsorbent bed and thereby decreases the separation capability,i.e reduces overall product recovery. Further, the crush strength ofadsorbent particles is decreased with high porosity/low densityadsorbent particles. This is a problem because adsorbent particles inthe bottom of large commercial PSA beds must resist crushing under theweight of thousands of pounds of adsorbent contained in the adsorbervessel.

As a means of increasing zeolite content in zeolite adsorbents it isknown to convert clay into zeolite via a process known as causticdigestion. It is also known that zeolite can be produced from preformedclay bodies, and that the shape of the preformed body can be retained.

Howell et al, in U.S. Pat. No. 3,119,660 disclosed a method of producingzeolite A, X and Y by forming kaolin clay into aggregates (also referredto as “massive bodies”) followed by calcination at 600-800° C. andcaustic digestion. They disclosed that this approach is particularlyuseful in aggregates having an increased clay content (in the range of20 to 80%) because the greater the clay content, the more zeolite isformed cheaply.

Howell et al also disclosed that inclusion of a void forming,combustible diluent substance facilitates the clay to zeoliteconversion, especially when the clay content is 50% or higher. This isbecause while clay is a non-porous material, zeolite is microporous, andtherefore void space is needed for expansion with such clay to zeoliteconversion.

The methodology of providing void space for volume expansion was furtherinvestigated by W. H. Flank et al (U.S. Pat. No. 4,818,508). Theydiscovered that the rate of zeolite formation in massive bodies can beaccelerated and the purity of zeolite enhanced by controlling the sizeof clay particles used to make the preformed bodies, together withaddition of pore generating materials and inert binder.

Leavitt (U.S. Pat. No. 5,074,892) states that NaX adsorbent crystals maybe treated with caustic to remove soluble, non-crystalline debris andenhance cation exposure.

S. M. Kuznicki et al disclosed a method to make X-type zeolite (U.S.Pat. No. 4,603,040) having a Si/A12 ratio of 2.0 (also referred to as“maximum aluminum X”). They extruded mixtures consisting of kaolin clayand 10 to 30% of a pore forming material into a preformed body. Aftercalcining this material at 600° C., the body was treated in an aqueoussolution of NaOH and KOH. Typically such treatment converts meta kaolininto type A zeolite as well as a high purity maximum aluminum X zeolite(2.0) product. Unfortunately, in the example an aluminum zeolite X (2.0)could only be made by maintaining the treatment temperature at about 50°C. for a period of 10 days.

Thus all the prior art related to caustically digested preformed Xzeolite was directed to making a massive body of high zeolite content.Further, the materials formed were high density low porosity materials(as a result of high clay content and resultant low macropore volume),even with the use of organic burn-out.

OBJECTS OF THE INVENTION

The objective of this invention is to enhance the intrinsic masstransfer rate of PSA adsorbents while minimizing and/or eliminating theneed for reduction in particle size. As a result, the materials of theinvention can be used in PSA processes that have high adsorbentproductivity and high process efficiency, short cycle times and lowpower consumption.

SUMMARY OF THE INVENTION

The invention preferably comprises an adsorbent material having an SCRRof greater than 1.2.

The invention preferably further includes a process for the separationof at least one first component from a gas mixture including said firstcomponent and a second less selectively adsorbable component using anadsorbent having an SCRR greater than 1.2.

The invention preferably includes a process of making an adsorbentcomprising the following steps:

a) providing zeolite powder having a predetermined composition;

b) mixing said powder with a binder capable of being converted tozeolite via caustic digestion, wherein said binder is added in an amountless than 20% by weight, preferably ≦15%, more preferably ≦12% of thepowder/binder mixture;

c) forming beads from said mixture;

d) calcining said beads;

e) caustically digesting said beads such that at least a portion of saidbinder is converted to zeolite;

f) recovering said adsorbent.

In further preferred embodiments, the process of making the adsorbentfurther comprises the steps of:

g) adding a combustible fiber or particulate material to thebinder/zeolite mix prior to bead forming.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages will occur to those skilled inthe art from the following description of preferred embodiments and theaccompanying drawings in which:

FIG. 1 is a schematic diagram showing the apparatus used to measureintrinsic adsorption rate.

FIGS. 2-4, 10-11, 15 and 20 are graphs illustrating porosimetry data(cumulative intrusion vs. sample diameter) for materials made accordingto the examples of the invention as well as comparison examples.

FIGS. 5-6 and 12-14 are SEM pictures (at 10,000×magnification) ofcross-sectioned adsorbent beads before caustic digestion and aftercaustic digestion as well as with fiber burn-out and without fiberburn-out;

FIG. 7 is a graph of SCRR vs. Porosity using the data from Table 1;

FIG. 8 is a graph of SCRR vs. Predigestion Binder Content using the datafrom Table 1;

FIGS. 9A and B are schematic drawings illustrating the macroporestructure within a bead of zeolite adsorbent before and after causticdigestion;

FIGS. 16 and 17 are SEM pictures (80×magnification) of cross-sectionedadsorbent beads before caustic digestion and after caustic digestion aswell as with fiber burn-out;

FIGS. 18 and 19 are SEM pictures (5000×magnification) of cross-sectionedadsorbent beads before caustic digestion and after caustic digestion.

DETAILED DESCRIPTION OF THE INVENTION

The instant invention is based upon the recognition by the inventor ofthe cause of slow intrinsic diffusion rate, and relates to a process forimproving the intrinsic diffusion rate in adsorbent materials. Inparticular, the invention is based on the recognition that mass transferrate is not a simple function of porosity or particle size, as suggestedby the prior art. For example, an adsorbent system may have a largemacropore volume and therefore large porosity, but still have a slowmass transfer rate. We have found that the structural features of theagglomerate macropores have a significant effect on the mass transferrate (e.g. the intrinsic rate of an adsorbent). Such relationship, orrecognition of intrinsic rate has not been previously disclosed orsuggested in the prior art. It is also noted that while the tortuosityof pores in an adsorbent has been previously discussed, the suggestionthat this may be controlled to effect adsorbent properties (e.g. masstransfer rate) has not been previously disclosed.

By the terms “sorption rate”, or “adsorption rate” or “rate” we mean therate at which the adsorbate loading changes in a given time period in anadsorbent particle for a given adsorption separation process. Thissorption rate is approximately proportional to the inverse of (particlediameter)² and is directly proportional to the “intrinsic sorption rate”(also referred to as the “intrinsic rate” or “intrinsic diffusionrate”). By the term “intrinsic rate” we mean that component of thesorption rate that is due to the intrinsic properties of an adsorbentparticle including, but not limited to, macropore diameter, macroporeshape, macropore volume, macropore distribution and the way macroporesare connected to each other within a particle. A material's intrinsicrate is independent of particle size. The term “relative rate” is acomparative measure of “sorption rate” and the term “size-compensatedrelative rate” (SCRR) is a measure of the intrinsic sorption rate.

In particular, SCRR is defined as

SCRR(p)=RR(p)*[d _(particle)]²  (1)

d_(particle) is the Ergun diameter derived from the particle sizedistribution, p is total pressure of the system and RR is Relative Ratewhich in turn is defined as

RR(p)=[ΔN ₂(Y _(F) , Y ₀)]/(t ₂ −t ₁)  (2)

Wherein

ΔN ₂(Y _(F) , Y ₀)=(N ₂ Loading at p, Y _(F))−(N ₂ Loading at p, Y₀)  (3)

Y is then composition of the stream defined in mole fraction of oxygen.t is time. Y_(F) is composition of feed which is 0.2, Y₀ is compositionof regeneration gas which is 1, t₂ is the time when Y₂ is equal to 0.3and t₁ is the time when Y₁ is equal to 0.9. The units for SCRR are[(mmol mm²)/(g sec) SCRR is disclosed in co-pending, co-filed andcommonly assigned U.S. patent application Ser. No. 9/622,867 (Mullhauptet al), the contents of which are herein incorporated by reference.

Adsorbent aggregates are formed by adhering microporous zeolite crystalstogether with binder materials. The micropores are due to thecrystalline structure of the zeolite, with X zeolites, for example,having micropores that are typically about 8A in diameter. The cationsof the zeolite (e.g. Li+) reside in the micropores of the zeolitecrystals.

Binders are dense materials which do not have adsorptive properties, butwhich are inserted to attach zeolite crystals. In order to functioneffectively, the size of binder particles must be much smaller than thesize of the individual zeolite crystals.

When crystals are aggregated with binder, void spaces or macroporesbetween the crystals on the order of 0.001μ to 10μ are formed.Macroporosity is determined by several factors including crystal sizeand morphology of the zeolite powder, particle size of binder, the watercontent of the mixture, as well as the force used in the aggregatingprocess. The parameters of pellet or bead formation processes aretypically determined by considerations other than controllingmacroporosity.

An example of the latter point is in Nauta bead formation, wherecompacting of the binder and zeolite generally results from the weightof adsorbent in the forming vessel. In large scale production, thecompacting force is much larger due to the increased size of theequipment utilized. Dictated by such uncontrollable reasons, theporosity of commercial products usually falls in a range of 0.30-0.38(or 30%-38%) (Wankat, P. C. Rate Controlled Separations; ElsevierApplied Science, 1990, p. 226).

Our research has shown that the distribution of binder in theagglomerate is a random process, with t majority of the binder particlesbeing in contact with single zeolite crystals or with other binderparticles. The fine particles of clay binder form a sponge-likestructure, with the diameter of the pores within this sponge structurebeing about the same order of magnitude as the clay particles. Thissponge-like clay structure bridges the gap between zeolite crystals,thus functioning as binder. Unfortunately, because the distribution ofbinder in the agglomerate is random, some of the clay sponge only coatthe zeolite crystals, but do not form bridges between the crystals,thus, at least partially, blocking the macropores. This adverselyeffects the mass transfer rate of the adsorbent.

As indicated above, the prior art has failed to recognize thecorrelation between the intrinsic properties of a zeolite agglomerateand its mass transfer rate. Thus, the invention comprises methods whichmay be used to improve the intrinsic mass transfer rate of adsorbentsagglomerated with binder by improving its macropore structure. For thepurposes of this disclosure, unless otherwise indicated, furtherreferences to pores are references to macropores.

The first method is to use an appropriate amount of agglomerate binderwhich may be converted into zeolite via caustic digestion (“CD”), andthe subsequent application of CD to convert the binder to zeolite afterbonding. The binder material is used in a specific range of amounts andmay be Kaolin clay or Kaolin-type clays including illite, levesite,dickite, nacrite, sipiolite or other materials which can be convertedinto zeolite such as holloysite clay, or alumino-silicate gels.

Because the prior art has only taught CD as a means to increase zeolitecontent as well as a means to substitute cheap clay for zeolite, theprior art suggestion has been that the amount of clay binder forconversion should be at least 20%. The reason for this is to maximizethe amount of relatively cheap zeolite formed from clay during the CDprocess. Further, prior to the invention, the zeolite content wasmaximized (via CD) in order to increase the capacity of the adsorbentmaterial. In contrast, there has been no teaching or suggestion in theprior art that CD may be an effective tool for controlling mass transferrate.

We have found that caustic digestion is an effective means to improvethe properties of an adsorbent only when the amount of binder is below20%, preferably 15%, more preferably 12% or even less than 10%. This isbecause too much binder (e.g. in amounts of 20 wt. % and above) createsexcessive zeolite growth which, while increasing the capacity of theadsorbent, interferes with its mass transfer rate by at least partiallyblocking its macropore system. Thus in contrast to the teachings of theprior art, the use of more clay to convert to zeolite is not necessarilybetter. We should note that binder content is measured as [(dry weightbinder)/(dry weight binder+dry weight zeolite)].

In fact, when the amount of clay is less than 20%, we have found thefollowing to be true. During CD a portion of the clay binder material istransported to the surface of zeolite crystals to form new zeolitecrystals. Those clay particles which were functioning in a true binderfunction became a new solid zeolite bridge between pre-existing zeolitecrystals. This process is accompanied by a reduction in macroporosity.

While not wishing to be bound by any theory, we also believe that thosebinder particles that previously blocked the macropores were dissolvedvia CD, thus opening previously blocked channels. In addition we believethat a further macropore restructuring occurs. In particular, it is ourbelief that many of the macropores in the clay containing zeolitespossessed what we refer to as an “ink-bottle” structure. Such porestructure has a narrow neck which opens into a much larger but enclosedarea and are illustrated in FIG. 9A discussed below. It is our beliefthat CD as practiced herein results in a recrystallization andredistribution of the zeolite crystals such that the narrow neckopenings were eliminated, resulting in a macropore system that is muchmore efficient than that originally present. This elimination of narrowneck openings simultaneously with the reduction in macroporosity isintuitively contradictory, and was unexpected especially in light of theprior art.

Finally, during CD the sponge pores between clay particles in the binderconsolidated to form large channels. Ultimately, what we refer to as atrunk and tributary pore system emerged. This new pore system is muchmore efficient in mass transfer than the original macropore system. Thisrestructuring of macropores by caustic digestion has not been previouslyreported and has great utility in PSA air separation. Indeed, the use ofCD to control the mass transfer rate of an adsorbent has not beenheretofore disclosed.

We should note that for the materials disclosed herein, by the term“trunk” we mean macropores having a diameter of greater than 0.1-1.0microns, and by the term “tributary” we mean macropores having adiameter of less than 0.1 microns. In a general sense, materialsdisclosed herein can be generally classified by their trunk to tributaryvolume ratio (TTVR) (that is the ratio of trunk pore volume to tributarypore volume).

Further, because clay is a dense phase and zeolite is a microporousmaterial the clay to zeolite conversion created new micropores at theexpense of the macropores of the aggregates. Thus, CD actually reducedthe macroporosity of the aggregates, a result which the prior art wouldsuggest is undesirable. This is because a decrease in macroporositywould be expected to reduce mass transfer rate.

A second means for improving intrinsic rate is by creating cylindricalpores having predetermined dimensions that areoriented radially withinthe adsorbent. Such pores connect the interior of a bead directly to itssurface and to the gas stream flow through an adsorbent bed.

The instant inventor conceived the idea of placing fibers having certaincompositions, dimensions and in certain concentrations into theadsorbent aggregates and then burning them out to create the cylindricalchannels in the 2-10 micron diameter range. The adsorbents made withfiber burn-out have a bimodal macropore structure. There has been noprior art disclosure with respect to the use or formation of suchchannels in adsorbent beads or pellets

We have found that it is desirable to use cut fiber with a length insame order of magnitude as the bead diameter. Thus for making 8×2 meshbeads, we use fiber of {fraction (1/32)}″ to ¼″, preferably ⅛″ to{fraction (1/16)}″ in length. The amount of fiber should be betweenabout 1% to about 15 wt %, preferably 2-10 wt. %, most preferably 4-6%.With respect to the thickness of fiber, we used fiber having a range of0.5 to 25 Denier (1 Denier=1 gm fiber/9000 meter of filament),preferably 1 to 5 Denier, and having a diameter of about 5 to about 50μ(Note that “μ”, “microns” or “micrometers” are used interchangeably inthis application).

It is also preferable to use hydrophilic fibers such as RAYON, NYLON orSISAL. However,weakly hydrophobic fibers such as polyester are alsouseful. The most preferred fiber was 1.5 Denier RAYON.

A third means of improving intrinsic diffusion rate is to useparticulate burn-out materials having a diameter in the range of 0.1-30microns and in amounts between 2-15 wt. % to extend the naturalmacropore system. Such material may include latex having a glasstransition temperature of>4° C., corn starch, or other fine combustiblematerials.

As the data set forth below demonstrates, the effect of this particulateburn-out in conjunction with caustic digestion has a greater effect onadsorbents having a bead diameter less than or equal to 1.6 mm, ascompared to materials having a bead diameter of greater than 1.6 mm.

A fourth method for improving the macropore structure is by controllingbinder (clay) distribution during bonding. We have found that the use ofa latex having a low glass transition point (e.g. less than 40° C.) anda particle size in the range of macropore diameter allows us to reducethe amount of required binder to levels previously thought to beineffective. It is preferable that the latex have a particle diameterless than 2 microns, preferably less than 1 micron. Preferred latexmaterials include UCAR 163 s having a particle diameter of 0.4μ andglass transition temperature of −11° C. or UCAR 193 having a particlediameter of 0.7μ and glass transition temperature of −36° C. The amountof latex is preferably 2-8 wt. %.

We found during our research that at a level of 6% kaolin, beadformation without the latex additive was not possible. In contrast, with6% UCAR 163 s, we were able to synthesize agglomerates using as littleas 6% Kaolin. Even at this level we were able to form beads of any sizeat high yields. Most surprising is that after calcination the beadsretained their physical strength.

When kaolin is used as binder, this forming method is even morebeneficial when used in conjunction with caustic digestion. As definedabove caustic digestion not only produced an enhanced trunk andtributary pore structure it also improved the physical strength of thebeads. Thus the use of latex provides for a method to improve macroporediffusion rate. In fact, the use of latex as described in method fourabove is applicable to any agglomerate system, not just those using abinder which can be converted to zeolite.

While Moreau mentions the use of pore forming organic material to swellthe agglomerate during baking, he fails to specify the types ofmaterials or size requirements necessary to accomplish his objective. Healso fails to disclose the use of CD or the effect of binder content onadsorbent properties In contrast, the present invention teaches how toincrease the mass transfer rate within the range of porosities exhibitedby conventional adsorbents.

Generally, the process of making our inventive adsorbents comprised thefollowing steps:

a) providing zeolite powder having a predetermined composition;

b) mixing said powder with a binder capable of being converted tozeolite via caustic digestion, wherein said binder is added in an amountless than 20% by weight, preferably ≦15%, more preferably ≦12% of thepowder/binder mixture;

c) forming beads from said mixture;

d) calcining said beads;

e) caustically digesting said beads;

f) recovering said adsorbent.

We should note that at least a portion of said binder should beconverted to zeolite during said caustic digestion step. In particular,it is preferred that at least 10% of the binder, preferably at least50%, more preferably at least 80%, and most preferably all orsubstantially all of said binder is converted to zeolite.

Preparation of materials characterizing the invention and forcomparative purposes is generally described below, with a more detaileddescription to follow in Examples 13-26.

More particularly, zeolite NaKX(2.0) powder obtained from UOP (DesPlaines, Ill. USA) was formed into beads using kaolin clay in amounts of30%, 20%, 15% and 12% as binder. Some samples also had fibers orparticulate materials also incorporated therein.

The beads were calcined to convert kaolin into meta-kaolin. In thosesamples containing fibers the fibers were combusted or burned out tocreate cylindrical channels within the beads. The thus prepared beadswere then treated with a caustic solution of either NaOH or a mixture ofNaOH and KOH to convert substantially all of the meta-kaolin binder intozeolite and to repair the damage to the zeolite inflicted by combustionof fiber. (As will be recognized by those of skill in the art, thecaustic solution can also be first cooked with X2.0 zeolite and kaolinclay to create a solution with a composition equal to the mother liquorused in X2.0 synthesis, then mixed with 20% fresh caustic solution to beused as the digestion solution. The purpose of using such a digestionsolution is to reduce dissolution of the beads and to recycle motherliquor.) The caustically digested or “CD” beads were Li ion exchanged togive LiX2.0CD adsorbent.

As indicated above, preformed X2.0 beads were prepared both with andwithout fiber burn-out. Each preparation of the beads was divided intotwo equal portions. One portion was Li ion exchanged without beingcaustically digested, such samples were designated BD (beforedigestion). The other portion was caustically digested, then Li ionexchanged. These samples were designated CD (caustically digested).

Both LiX2.0BD and LiX2.0CD were studied and the results compared. Thepore structure of both materials was studied and characterized usingmercury porosimetry and scanning electron microscopy (SEM). With respectto the porosimetry measurements, a Micromeritics AutoPore III 9420porosimeter was used.

The adsorption rate was measured using an adsorption rate apparatus andbreakthrough experiment described below. One skilled in the art willrecognize that variations of this experiment may be used as long as theguiding criteria are followed.

For the process of air separation, a breakthrough test is performed intwo steps in which the flow rate, pressure and temperature of the feedgas are the same in both steps. With reference to FIG. 1, this processwill be described. The first step involves saturation of the adsorbentbed 1 with O₂ the least selective component provided via flow meter 2and line 3. In the second step, air or a synthetic air mixturecontaining N₂ and O₂ is then introduced to bed 1 via flow meter 4 andline 3. Valve 6 operates in conjunction with flow meter 2 such thatpressure of the air or synthetic air is maintained in an external loopuntil the four port valve 7 connects the air/synthetic air feed to line3 such that the air/synthetic air flows into bed 1. The pressure,temperature and composition of the feed mixture in the second stepshould be representative of that in an adsorption step of an actualprocess, e.g. 1.5 bar, 300° K and feed air composition. The molar fluxwas approximately 10 mol/m² s, although this flux may be varied asrequired. The pressure is maintained substantially constant in the bed 1by using a control valve 8 located on the downstream side of theadsorbent bed. The endspace and connecting piping volumes (dead volumes)are designed to be 5% or less than that of the adsorbent bed volume(approximately 20 cm³).

The flow rate and concentration of O₂ are continuously and accuratelymonitored throughout step two via flow meter 9 and oxygen analyzer 10until the breakthrough of N₂ is complete. Flow to analyzer 10 ismaintained at a fixed amount via fixed valve 5. In step two, the moreselectively adsorbed N₂ displaces the adsorbed O₂ already in the bed 1.As the bed nears saturation with the air mixture, the breakthrough of N₂is reflected in a decrease in the O₂ concentration and an increase inoverall flow rate of the effluent from the bed. The piping and adsorbentbed are maintained at the same temperature as the feed by immersing themin a thermostat bath controlled at the same temperature as the feed. Therelative rate and SCRR are determined from the results of this test. Thedifferential loading (appearing in equation 2) of ΔN₂ is determined froman analysis of the breakthrough results. The T₂-T₁ in equation (2) isdetermined directly from the oxygen concentration front measured at theexit of the test bed (using oxygen analyzer 10). The relative ratecalculated from equation 2 is used in equation 1 with the particle sizeinformation to determine SCRR.

The data obtained from the porosity and rate measurements is discussedbelow, and detailed in Table 1.

TABLE 1 Description of Before Digestion Materials (BD) Sample BinderBead Porosity Median Pore # Content Additive Content Size in % Diameterμ TTVR SCRR 1 30% 5% 2.5 Denier Rayon 8 × 12 0.209 2 20% No fiber 8 × 123 20% No fiber 8 × 12 28.94 0.007 0.027 0.222 4 20% No fiber 8 × 1228.70 0.008 0.027 0.275 5 20% 6% 5.5 Denier Rayon 8 × 12 34.49 0.0130.115 0.329 6 20% 4% 1.5 Denier Rayon 8 × 12 7 20% 6% 1.5 Denier Rayon 8× 12 8 20% 3.5% 7 Denier Nylon 8 × 12 9 15% No fiber 8 × 12 30.97 0.0120.055 0.367 10 15% 6% 5.5 Denier Rayon 8 × 12 36.89 0.018 0.080 0.461 1115% 6% 2.5 Denier Rayon 8 × 12 42.64 0.028 0.090 0.757 12 15% 6% 1.5Denier Rayon 8 × 12 36.72 0.016 0.053 0.425 13 15% 7% Corn starch 8 × 1237.97 0.018 0.056 0.363 14 12% No fiber 8 × 12 34.57 0.020 0.020 0.37615 12% No fiber 8 × 12 34.56 0.016 0.036 0.397 16 12% No fiber 8 × 1234.26 0.023 0.147 0.358 17 12% 6% 5.5 Denier Rayon 8 × 12 38.88 0.0320.089 0.889 18 12% 4% 2.5 Denier Rayon 8 × 12 38.00 0.021 0.061 0.441 1912% 6% 2.5 Denier Rayon 8 × 12 20 12% 6% 1.5 Denier Rayon 8 × 12 35.400.029 0.077 0.660 21 12% 6% 1.5 Denier Rayon 8 × 12 22 12% 6% 1.5 DenierRayon 8 × 12 23 12% 6% 1.5 Denier Rayon 8 × 12 24 12% 6% 1.5 DenierRayon 8 × 12 25 12% 6% 1.5 Denier Rayon 8 × 12 26 12% 7% Corn starch 8 ×12 37.00 0.022 0.047 0.400 27 12% 6% 1.5 Denier Rayon 12 × 14  28 12% 6%1.5 Denier Rayon 12 × 14  29 12% 7% Corn starch 12 × 14  30 12% 7% Cornstarch 12 × 14  Description of Caustic Digested Materials CD) SamplePorosity Median Pore # in % Diameter μ TTVR SCRR 1 0.573 2 26.06 0.4303.190 0.602 3 25.46 0.157 1.719 0.709 4 23.60 0.367 7.160 1.093 5 30.040.441 4.389 0.825 6 25.39 0.444 5.534 1.103 7 31.35 0.450 6.689 1.361 81.632 9 29.60 0.468 8.626 1.227 10 34.54 0.475 6.604 1.800 11 39.740.490 6.117 2.015 12 36.85 0.457 7.140 1.770 13 34.60 0.360 5.100 1.39814 34.70 0.530 11.468 2.371 15 30.43 0.400 6.320 1.568 16 32.79 0.4306.224 1.837 17 36.24 0.460 6.765 2.232 18 1.689 19 39.72 0.520 12.5612.440 20 21 35.59 0.440 6.929 2.023 22 38.60 0.450 6.018 2.391 23 35.380.490 8.229 1.851 24 35.09 0.480 6.270 1.970 25 35.91 0.470 7.360 2.00026 35.60 0.380 5.936 1.810 27 36.48 0.450 5.715 1.410 28 35.32 0.4606.629 1.490 29 33.28 0.550 16.058 1.950 30 36.04 0.470 7.510 1.860

The first finding of note was that the porosity of the CD beads is lessthan the BD beads. This is not unexpected because as the meta kaolinconverts into zeolite it expands into, and takes over the macroporespace, thus reducing the porosity. We should note that by the term“porosity” we mean that fraction or percentage of bead volume that isoccupied by macropores and is determined by mercury porosimetry.

The porosity reduction for samples made with 20% kaolin binder is setforth in the following example.

EXAMPLE #1

The sample numbers below reference Table 1, wherein each sample numberrepresents a batch of NaKX2.0BD precursor (e.g. 3BD and 3CD were madefrom the same batch; 4BD and 4CD were made from the same batch, etc.).

Samples 3 and 4 (BD and CD) were studies with the results listed inTable 1. The average porosity of BD samples is 28.9% and for CD samples(including Sample 2) is 25.76%.

All these samples have a uni-modal pore system. The averaged medianmacropore diameter (calculated according to its contribution to volume)for BD samples is 0.0074μ and for CD samples is 0.32μ.

FIG. 2 shows a plot of pore volume (cumulative intrusion of mercury intopores of diameter between 0.002μ to 2μ) vs. diameter for Sample 3 (BDand CD). The narrow distribution of pore diameters and its concentrationin the very small pore diameter range suggests the wide existence ofink-bottle macropores in the BD sample. The increase of pore diameter byCD suggests consolidation of macropores to form trunk pores and theopening up of the ink-bottle bottlenecks. The TTVR of 3BD is <1 and for3CD is 1.7. The TTVR values of individual samples are listed in Table 1.

For beads made with 15% kaolin the porosity results are set forth inExample 2.

EXAMPLE #2

Sample 9 (BD and CD) was measured, with the porosity being 30.75% and29.6%, respectively. Again caustic digestion reduced the porosity, butthe porosities of these samples are still higher than samples made with20% clay.

As discussed above, this is because the excess binder creates excessivezeolite growth that at least partially fills the macropores and reducesporosity and reduces rate. These samples have uni-modal pores.

FIG. 3 plots the cumulative intrusion volume vs. diameter for thesesamples. Again most of the macropore volume of BD beads is in the0.0001μ to 0.01μ range with the median pore diameter being 0.012μ.

After caustic digestion, the majority of macropores registered at 0.4μwith a median pore diameter of 0.47μ. In contrast recall the CD samplesof Example 1 which had an average pore diameter of 0.32μ and a wide porediameter distribution. As will be shown, the rate of sample 3CD isslower than sample 9CD.

The data illustrates that higher binder content makes caustic digestionless effective. The TTVR of these 15% clay CD samples are also largerthan their 20% clay counter parts (8.6 vs. 5.5).

For beads made with 12% clay, the porosity results are set forth inExample 3.

EXAMPLE #3

Three pairs of samples made with 12% kaolin were studied (Samples14-16). The results are listed in Table 1. The pore diameterdistribution of Sample 14 (BD and CD) is plotted in FIG. 4.

The averaged porosity of the BD beads is 34.5% and of the CD beads is32.6%. Once again, the caustic digestion reduced the porosity of thebeads. The reduction of binder content also further increased theporosity of the beads (as compared to those samples with higher bindercontent).

FIG. 4 shows that both 14 BD and 14CD are uni-modal. Once more, the BDsample has all its pore volume detected as pores with a very smalldiameter, with the median diameter being 0.02μ. Caustic digestionshifted the median pore diameter to 0.53μ. The TTVR of samples 14 BD and14 CD are 0.02 and 11.5. The TTVRs are listed in Table 1.

Sample 14 (BD and CD) was also characterized via SEM measurements (SeeFIGS. 5 and 6, respectively). The samples were prepared using a “pottedcross-section” procedure. First, the macropores of the adsorbent beadswere filled with epoxy. After the epoxy was cured, the beads werecross-sectioned then polished. To enhance the quality of the SEM image,a layer of epoxy on the cross-sectioned plane was removed by oxygenplasma bombardment.

With respect to FIG. 5 because the macropores were so small, thepenetration of epoxy into the sample was poor. The fact that we wereunable to get a sharp SEM image of the BD sample is indicative of thepresence of ink-bottle pores. As a result, the boundaries of zeolitecrystals in the macropore are fuzzy and the boundaries of clay particlesare not sharply defined as shown in FIG. 5.

FIG. 6 is an SEM picture of 14CD. Since caustic digestion clears awayclay and opens up the macropores, a good quality image is obtained. Thezeolite crystals are sharply defined and the macropores are wide openand without obstacles created by clay. The SEM results demonstrate thatcaustic digestion as practiced in this invention created a trunk poresystem.

The data presented above is summarized in Table 2 below:

TABLE 2 Averaged porosity (in %) of 8 × 12 beads BD CD No fiber No fiber20% kaolin 28.94 25.76 15% kaolin 30.97 29.5 12% kaolin 34.46 32.6

The processes described above had a significant effect upon the masstransfer rate of the adsorbent.

The extent of the adsorption rate improvement caused by causticdigestion was unexpected, especially in light of Moreau's suggestionthat one should increase, not decrease, porosity. In particular, interms of SCRR, caustic digestion improved the air adsorption rate by afactor of 3 to 6. The average value of SCRR of samples studies are: forBD 8×12 beads made with 20% clay 0.249 (versus 0.80 for CD beads). Forbeads made with 15% clay, the caustic treatment increased SCRR from 0.37(BD) to 1.227 (CD). For beads made with 12% clay, SCRR increased from0.377 (BD) to 1.925 (CD). The particulars are set forth below inExamples 4 and 5.

EXAMPLE #4

SCRR measurements were made using the apparatus described above.

SCRR measurements were conducted on LiX2.0BD samples 3 and 4; 9 and14-16. Results are listed in Table 1. The averaged SCRR increased from0.22 to 0.37 to 0.38 as the clay content dropped from 20% to 15% to 12%.The porosity of the samples increased from 28.91 (samples 3 BD and 4 BD)to 30.97 (sample 9 BD) to 34.46 (samples 14BD and 16BD). The median porediameter of all of these samples in the range of 0.01 microns. The TTVRvalues are all <1.

The SCRR of the these BD samples was not substantially effected by thebinder level change and porosity change, especially as binder reducedfrom 15% to 12%. The rate of all these samples is considered very lowwhen compared to caustic digested and fiber added samples.

EXAMPLE #5

SCRR measurements were conducted on LiX2.0CD samples made without anyburn-out additives. Most of them have counterpart BD samples tested inExample 4. These samples are 2CD, 3CD, 4CD (20% kaolin); 9CD (15%kaolin); and 14CD-16CD (12% kaolin). The results are listed in Table 1.

The averaged porosity of the CD samples is smaller than their BD counterparts. They are 25.76% (20% clay), 29.6% (15% clay) and 34.7% (12%clay). However their TTVR values are all larger than 2.

Their averaged SCRR values are 0.80, 1.23, and 1.93 (respectively), i.e.3.6 times, 3.3 times and 5.2 times larger than their BD counter parts(See Table 3). Thus even though CD produced a decrease in porosity, theSCRR of all these samples was greatly increased, a direct measure of theincrease in the mass transfer rate of gas through the macropores. Themedian pore diameters and TTVR of all samples show parallel increases.

TABLE 3 (SCRR Comparison) BD CD No fiber No fiber 20% Kaolin 0.249 0.8015% Kaolin 0.367 1.227 12% Kaolin 0.377 1.925

While binder reduction alone increases adsorption rate (SCRR), suchincrease is minimal compared to that achieved through the combination oflow binder content with CD. The effect of CD and binder content on masstransfer rate has not been recognized previously.

FIG. 7 illustrates the effect of SCRR vs. Porosity using the data inTable 1. As can be seen, materials having similar porosities can havesignificantly different rates. Thus there is not a direct correlation ofrate to porosity. Furthermore, rate changes of as much as a factor often are obtained while maintaining porosity within the normal range ofcommercial adsorbents.

While caustic digestion has reduced the porosity of the adsorbent, itactually has improved the quality of the resultant pore structure. Thisaccounts for the increase in SCRR for the CD samples.

FIG. 8 illustrates the effect of SCRR vs. Binder Content at thepredigestion stage using the data of Table 1.

Table 1 and FIG. 8 show that for aggregates made with binder contents of20% or more, even after caustic digestion, the adsorbent will still havea comparatively slow rate. On the other hand, the data clearlyestablishes that a reduction of binder content in conjunction with CDsignificantly increases SCRR.

An examination of the porosity data reveals that caustic digestionincreased the median macropore diameter from a range of about 0.1μ range(BD) to about 0.4μ range (CD) even though the overall porosity wasreduced. Furthermore, the distribution of pore volume for CD materialshaving less than 20% binder, is also quite narrow as compared tonon-caustically digested materials.

As discussed above, we believe that median macropore diameter andmacropore size distribution are indicators of the “quality” of theporosity. In other words a more efficient macropore system has been.

While not wishing to be bound by any theory, we believe that the medianpore diameter shift induced by caustic digestion resulted in part fromthe dismantling of the clay structures obstructing the macropores.Consistent with this theory is the theory that the recrystalizationprocess induced by caustic digestion opened up many ink-bottle poresystems, thus improving the quality of the connection of the macropores.

Ink bottle pores are characterized by a large central void with having anarrow entry path (or bottleneck) such that the pore resembles the shapeof an ink bottle. The formation of ink-bottle pores could be due tobinder. It also could be due to small zeolite crystals which whilehaving adsorptive capacity may, at least partially, block themacropores. Thus it is our belief that during caustic digestion thosesmall clay and zeolite particles creating the bottleneck arecontinuously dissolved and recrystalized into new zeolite crystals atnew locations. As a result the necks of ink-bottles are opened up. Inkbottle systems both before and after treatment are illustrated in FIGS.9-A and 9-B.

The presence of ink-bottle pores is not easily detectable by mercuryporosimetry measurements, which are typically utilized co measureporosity. This is because the measurement assigns a pore diameter to thepore volume based on the mercury pressure (e.g. mercury porosimetry datareflects the diameter of the bottleneck, not the bottle), Thus if a beadhas many ink-bottle pores, the mercury porosimetry data may provide amisleading impression. A full evaluation of our data, including SEMpictures suggested that extensive ink-bottle pore systems with bottlenecks in the 0.01 to 0.02μ range existed in the LiX2.0BD beads describedabove.

Through the increase of median pore diameter and removal of bottleneckpores, we believe caustic digestion created a trunk and tributary poresystem, (e.g. a system having large central (“trunk”) channels having adiameter 0.1-1.0 microns with attached “tributary” channels having adiameter of <0.1 microns). The qualitative change of the macroporestructure brought forth by CD is clearly demonstrated by SEM. Now wewill attempt to describe this change more quantitatively.

As indicated above, to measure the quality of the macropore system wedefined a parameter called the Trunk to Tributary Volume Ratio (TTVR)for a given adsorbent bead/pellet. Our experimental results usingzeolites having a single type of morphology have shown that CD sampleswith a measured median pore diameter of 0.1μ or less have a poor rate.As such these are less effective as trunk pores. We should note thatthis trunk to tributary transition diameter may change when zeoliteshaving other types of morphology are used. Indeed, the methodology ofthis invention would be expected to be effective with agglomerates madefrom any zeolite powder, regardless of morphology, or variationstherein. We note that the TTVRs for BD beads in the examples of theinstant invention are all less than 1.

As discussed above to provide direct evidence of the above we examinedour sample pairs (CD vs. BD) with SEM. The findings support ourassertions above.

1. In BD samples the fine particles of clay binder formed a sponge-likemass (see e.g. FIG. 5). The mass bridges the gap between zeolitecrystals, thus functioning as binder. However, a portion of the clayonly partially bridges the gaps between zeolite crystals, thuspartitioning the macropores of the beads and creating ink bottle pores.Further, the fact that the diameter of the pores in the sponge-likematerial has the same order of magnitude as the clay particles, explainswhy SD samples have a median pore diameter in the 0.01 to 0.02μ range.

2. Caustic digestion converts clay into zeolite. As suggested above,when the clay that completely bridges the gaps between crystalsundergoes the conversion, zeolite bridges remain adding physicalstrength to the zeolite.

Further, the pores in the clay sponges are consolidated by the CDprocess into the existing macropores, resulting in the formation of thetrunk pores referred to above. Finally, when the proper amount of binderis used, the bottlenecks of the ink-bottle pores are, at leastpartially, eliminated (See e.g. FIG. 6). Thus porosimetry data obtainedon CD samples represents a more accurate indication of pore sizedistribution that for BD samples.

However, when clay is converted into zeolite crystals, the newly createdzeolite crystals occupy a larger volume within the bead than theoriginal clay, thus contributing to the narrowing of the macropores.This is where the amount of original binder is significant. As statedabove, we have found that with amounts of 20% and above, the conversionto zeolite via CD has detrimental effects upon the macropore system andconsequently the mass transfer rate of the material. Simply put, toomuch zeolite is formed, thus blocking the macropores. While CD doesresult in dissolution and relocation of some zeolite that was previouslyblocking pores, there is a limit to this effect where there is excessiveclay/converted zeolite. The fact that CD effects the rate of masstransfer has not been heretofore recognized, nor has the fact that theamount of binder used for conversion is significant.

As discussed above, the use of fiber burn-out can also enhance masstransfer rate within an adsorbent. In particular, the use of thisprocess enhances formation of the trunk and tributary macropore systemdiscussed above and creates large open channels which directly connectthe space outside of beads with the interior of the beads (or pellets).

To make beads, the fiber was first mulled with the mixture of zeoliteand clay with a small amount of water. After mulling for 1-2 hours, themixture was transferred to a Nauta mixer for bead forming. To oursurprise the fibers assumed a parallel orientation within the beads. Asa result of this orientational preference, the beads formed are moreellipsoidal than spherical, especially for beads smaller than 8×12 mesh.

Another surprising result was that a large number of fibers actuallybroke through the surface of the beads (especially after causticdigestion) to provide an open path from center of beads to exterior ofthe beads. Finally, the amount of fiber we were able to incorporate intoeach bead was surprising. For example the incorporation of 6 wt % of 1.5Denier ⅛″ RAYON into the formulation results in more than 200 fibersbeing present in each 8×12 bead.

As discussed above, fiber containing beads were calcined at 600° C. anddivided into two portions. The first was Li ion exchanged directly togive LiX2.0 BD and other half was caustic digested then Li ion exchangedto give LiX2.0CD.

As seen in Table 1, fiber burn-out generally increase the porosity ofthe beads. Examples using 20% clay in conjunction with fiber burn outare described below in Example 6.

EXAMPLE #6

One LiX2.0BD and four LiX2.0CD samples of 8×12 beads, all of them weremade with 20% kaolin clay binder, but each containing fibers ofdifferent Denier were studied. Samples 5 (SD and CD) are a pair with thesame precursor. Results are listed in Table 1.

The fiber burn-out created a new group of pores with a diameter in thevicinity of 10μ. By incorporating 6% 5.5 Denier rayon, it also increasedporosity of BD beads by about 20% and CD beads by 12%. The porosity ofthe BD beads is 34.49% and the average of which of CD beads is 28.9%.

FIG. 10 shows a plot of cumulative intrusion volume vs. diameter forLiX2.0 samples 5BD and 5CD. The porosimetry data of the BD samplesuggests that it has a smooth and wide pore distribution from 0.0001μ to10μ. However the SEM data shows there are dead ended cylindricalchannels with discrete pores in, 10μ range. This suggests that mercuryporosimetry has misrepresented the pore diameter distribution, that isthe presence of ink-bottle pores masks the presence of larger pores.

FIG. 10 also shows that caustic digestion opened up some ink-bottlepores, which appear in the CD plot as 10μ pores. At the same time aportion of the pores in the 0.01 micron range were increased to becomepores with diameters narrowly centered around 0.4μ. The TTVR of sample5BD is <1 and of sample 5CD is 4.4. The TTVR values of individualsamples are listed in Table 1.

As with fiber free materials, caustic digestion reduced the overallporosity of the fiber containing BD materials (e.g. those containing 20%binder), in this case to 30.04% for sample (5CD).

Examples using 15% binder in conjunction with fiber burn-out aredescribed below in Example 7.

EXAMPLE #7

Three pairs of 8×12 samples made with 15% kaolin and rayon fiber ofdifferent Denier were studied. Results are listed in Table 1.

For beads made with 15% clay, 6% fiber increased porosity of DD beadsfrom 30.97% (Sample 9BD) to 35.5% (average of 10BD-12BD) and porosity ofCD bead from 29.56 (without fiber) (9CD) to 36.13% (with fiber).

The plots of pore diameter vs. cumulative intrusion volume for 12BD and12CD are given in FIG. 11.

The samples show a bi-modal pore distribution. The larger pores arecentered around 2.5μ and the smaller pores are centered around 0.01μ. AsFIG. 11 shows, the caustic digestion narrowed the pore distribution andmoved the center of the distribution of the larger pores to 7μ and thesmaller pores to 0.4μ. The median pore diameter of the BD beads is0.0164μ, and of the CD beads is 0.48μ.

The reduction of binder level from 20% to 15% has increased the medianpore diameter to the 0.4μ range. The TTVR of samples are listed inTable 1. The recrystalization induced by CD increased TTVR from <1 toabout 6.6 (average).

We also analyzed samples 12BD and 12CD via SEM. The results of the SEMstudy are given below:

It is our belief that fiber burn-out facilitates the penetration ofepoxy in the larger channels. As such we were able to get sharp imagesof zeolite crystals and clay particles in some locations of sample 12BD.But for much of the remaining surface, a diffuse picture was obtained(FIG. 13). In FIG. 12 the structure of the clay binder is clearlydepicted. The clay particles form sponge-like structures, dividing themacropore into smaller pores, producing narrower passages in themacropore. FIG. 14 is an SEM of sample 12CD. As with previous examplescaustic digestion restructures the macropore system to enlarge themacropores.

EXAMPLE 8

For beads made with 12% clay, 6% fiber increases porosity of the BDsamples from 34.46% to 37.32% and of the CD samples from 32.6% to36.34%.

Three BD samples and nine CD samples (three pairs) with 12% kaolin andvarious rayon fibers (burned out) were studied. Results are given inTable 1.

The averaged porosity for CD samples is 35.46% (samples 19CD, 21CD-25CD)compared to 32.6% for corresponding beads without fiber burn-out(average of 14CD-16CD). The pore diameter distribution of 26CD is givenin FIG. 15.

The existence of bi-modal pores is clearly demonstrated in FIG. 15.Because 1.5 Denier fibers were used, the pores created by burn-out weresmaller, their diameters being in the 7μ range. The pore diameterdistribution of the second mode still centers around 0.4μ. Thepersistence of 0.4μ pores may represent the diameter of the mainstacking pores created by zeolite powder.

The TTVR results are listed in Table 1. CD increased their value from <1to 7.7.

Samples 20BD and 25CD were also characterized by SEM.

FIG. 16 is a low magnification (80×) SEM picture of cross-section of abead of sample 20BD. It shows fiber burn-out created many “super”macropores. These pores are a new level of trunk pore above macropores.FIG. 17 is picture similar to that of FIG. 16, but after CD. It showsthe fiber burn-out pores remain intact after caustic digestion.

FIG. 18 gives a high magnification (5000×) SEM picture of 20BD in aregion neighbouring a fiber burn-out pore. Zeolite crystals are wellresolved. The magnification of this picture is not high enough to showindividual clay particles; however, it clearly depicts the sponge-likestructure formed by clay particles. It also illustrates how the spongelayer of clay partitions the macropores to form ink bottle pores.

FIG. 19 is an SEM picture of 25CD at 5000×magnification. The claystructure has disappeared and micropores are clean and open. Once againSEM depicts that caustic digestion is capable of opening up pores andestablishing trunk pores. Again, however, it is noted that the porosityof the CD materials is less than that of the BD materials.

The averaged porosity (in percent) of all 8×12 beads from Table 1 is setforth in Table 4.

TABLE 4 (POROSITY VS. CLAY CONTENT) BD CD No fiber Fiber No fiber Fiber20% 28.94 34.49 25.76 30.7 Kaolin 15% 30.97 28.75 29.5 36.13 Kaolin 12%34.46 37.32 32.6 36.34 Kaolin

As shown above, the introduction of fiber burn-out creates a bi-modalpore distribution such that a new group of pores having a diameter ofabout 7-15μ is created (in addition to the pores already present). Thedata in FIG. 15 suggests that a large portion of the channels created byburn-out actually are detected by mercury porosimetry. For beads madewith 12% clay, 6% 1.5 Denier ⅛″ rayon these newly created porescontribute to about 10-20% of the total macropores. These larger fiberburn-out pores, provide a network of accessability to the smaller poresin the bead. For BD fiber samples, like their counterparts withoutfiber, the median pore diameter is in the 0.01-0.02μ range (which againsuggests the existence of ink bottle pores and clay binder sponge). ForCD beads, the median pore diameter is in the 0.4-0.5μ range.

The average Median Pore Diameters of 8×12 beads from Table 1 is setforth in Table 5.

TABLE 5 (AVERAGE MEDIAN PORE DIAMETER VS. CLAY CONTENT) BD CD No fiberFiber No fiber Fiber 20% 0.0079 0.013 0.32 0.45 Kaolin 15% 0.012 0.0210.47 0.47 Kaolin 12% 0.02 0.03 0.45 0.50 Kaolin

The median pore diameter of the CD samples is all clustered in a verynarrow range, 0.45-0.50μ. We believe this is the natural macroporediameter created by the stacking of zeolite particles. At a 20% orhigher clay level, the median pore diameter dropped, we believe due tothe excessive amount of zeolite formed and the creation of ink bottlepores.

The averaged TTVRs of 8×12 beads data from Table 1 is set forth in Table6.

TABLE 6 (TTVR VS. CLAY CONTENT) BD CD No fiber Fiber No fiber Fiber 20%<1 <1 4.0 5.53 Kaolin 15% <1 <1 8.6 6.6 Kaolin 12% <1 <1 8.0 7.7 Kaolin

As in the case of median pore diameter, CD increased the TTVR ofmaterials and brought them into a narrow range of values. TTVR is a yardstick for measuring the success of the creation of a trunk and tributarymacropore system. Both median pore diameter and TTVR are indicators ofmacropore conditions. SCRR is the best overall indicator for masstransfer rate.

The effect of the above discussed methods on mass transfer rate will nowbe discussed in the following Examples, with reference to Table 1.

EXAMPLE #9

SCRR measurements were conducted on LiX2.0BD samples made with varietyof fiber burn-out and different level of kaolin clay. These samples are:1BD (30% kaolin), 5BD (20% kaolin), 10BD-12BD (15% kaolin) and 17BD-19BD(12% kaolin). Results are listed in Table 1.

The averaged SCRR values for each group are 0.21, 0.33, 0.55, 0.66,respectively. Comparing to their counterpart samples without fiber inExample 4, they are significantly faster. However, the CD samples withno fiber burn-out (from Example 5) are more than three times faster thanthe BD samples of this Example. The cylindrical pores created by fiberburn-out provide a structure of “super” trunk pores. However, as seenfrom the porosimetery measurements many of them are only partiallyopened. In addition, the median pore diameter of these samples aremeasured in 0.01 micron range, i.e. the trunk macropores are still atleast partially blocked. The TTVR values all less than 1. Withobstructed macropores, the super trunk pores have only limited use andeffect upon mass transfer rate.

EXAMPLE 10

SCRR measurements were conducted on LiX2.0CD samples made with varietyof fiber burn-out and different level of kaolin clay. These samples are1CD (30% kaolin), 5CD-8CD (20% kaolin), 10CD-12CD (15% kaolin) and17CD-25CD (12% kaolin). Results are listed in Table 1.

Again, caustic digestion improved SCRR significantly with respect to theBD samples. The average SCRR values of these CD samples are: 0.57 (30%binder), 1.20 (20% binder), 1.86 (15% binder), 2.1 (12% binder). The 12%kaolin samples have highest SCRR, averaging 2.05. Caustic digestion hascleaned up both the fiber burn-out pore and zeolite stack pores. On theother hand, the samples made with 30% clay, even with fiber burn-out andcaustic digestion, still had an SCRR of only 0.57. This shows that fiberburn-out and caustic digestion are useful but only with lower bindercontents of less than 20%.

A comparison of averaged SCRR of 8×12 beads taken from Table 1 is shownin Table 7:

TABLE 7 (SCRR VS. CLAY CONTENT) BD CD No fiber Fiber No fiber Fiber 30%no data 0.209 no data 0.573 Kaolin 20% 0.249 0.329 0.80  1.27 Kaolin 15%0.367 0.548 1.227 1.86 Kaolin 12% 0.377 0.66  1.925 2.15 Kaolin

By way of comparison, a sample of NaX(2.3) having 12% attagel binder(which is not capable of conversion to zeolite) has an SCRR of 0.596. Asample of LiX(2.5) having 12% attagel binder had an SCRR of 0.447.

The average values of SCRR in the Table above clearly demonstratecaustic digestion, fiber burn-out and low clay content are significantvariables to rate improvement, especially when used in combination.

As discussed above, the addition of corn starch was also investigated.

EXAMPLE 11

A pair of samples made with 7% corn starch burn out and 15% kaolin (13BDand 13CD) were studied. The porosimetry data is listed in Table 1, andtheir pore diameter distributions are plotted in FIG. 20. As expected,CD reduced porosity of the sample from 37.97% to 34.6%. Results of 13CDshow that corn starch burn-out does not introduce a bi-modal porestructure. The pores of the CD samples have a median pore diameter of0.36μ. The porosity is 34.6% compared to 29.6% for its counterpartwithout any burn-out. The TTVR of the pair are <1 and 5.1, respectively(Table 1).

EXAMPLE #12

SCRR measurements were conducted in Samples 13BD and 13CD. Resultsshowed that the SCRR of the BD sample was 0.363, which was about thesame as the sample without burn-out (9BD: SCRR=0.367). The SCRR of theCD sample was 1.398 was lower than the samples with fiber burn-out(10CD-12CD).

Indeed, when the diameter of the beaded products are in the 2.0 mmrange, the average of the four samples formed with 12% clay and 7% cornstarch burn-out is 1.81 which is lower than 2.12 for beads formed with6% fiber burn-out. Surprisingly, however, the difference was reversedwhen a bead size of 12×14 mesh or smaller was used. For beads 12×14 meshin size the SCRR of beads formed with 12% clay and 7% corn starchaveraged 1.90 compared to 1.45 for beads formed with 12% clay and 6%fiber burn-out as illustrated in Table 8.

TABLE 8 SCRR of LiX2.0 CD beads formed with 12% clay plus: 7% cornstarch 6% RAYON  8 × 12 1.81 2.12 (avg.) 12 × 14 1.90 (avg.) 1.45 (avg.)

The non-limiting examples below set forth procedures used for makingadsorbents referenced in Table 1. We should note that although theexamples recite LiX as the adsorbent material, the methods of theinvention are equally applicable to other adsorbent materials such astype A and other naturally occurring zeolites and zeolites containingmonovalent, multivalent or mixed cations.

EXAMPLE #13

NaKX(2.0)/20% Binder

2500 gm dry weight (3924.6 gm wet weight) NaKX2.0 powder (supplied byUOP) and 625 gm dry weight (745.0 gm wet weight) of ECCA Tex-611 clay (apurified kaolin clay supplied by ECC corp.) were mixed together in a LFSimpson Mix-Muller (supplied by National Engineering Co.). Water wasadded at a rate of 10 ml/min. for the first 15 minutes, and at the rateof 4 ml/min. for next 50 minutes. The wet mixture was mulled for 55 moreminutes without adding water.

The mulled mixture was transfered to a DBY-10R Nauta Mixer (supplied byHosokawa Micron Powder Systems) for mixing for about one hour. The lumpswere broken down to return the mixture to powder state. Then, water wasadded slowly by an atomizer. As the moisture of the mixture increased,beads start to form. The beads growing was stopped by adding driedbonding mix at the point when highest yield of 8×12 size beads could beharvested.

The mixture of different size beads was dried in air overnight thencalcined in a Blue M oven with dry air purge. The oven temperature wasramped up to 600° C. in 2 hours and maintained at 600° C. for 2 hours.

The calcined bead was screened into cuts of different size. Most ofstudies reported here were conducted on the 8×12 fraction. The bondedbeads made in this example contain 20% binder and are named NaKX2.0BD,where BD stands for before digestion.

EXAMPLE #14

NaKX(2.0)/15% Binder

2500 gm dry weight of NaKX2.0 (wet weight 3968 gm) and 441.4 gm dryweight of the ECCA Tex-611 (wet weight 522 gm) were mulled in muller andwater was pumped in 10 ml/min for 15 min.; then 4 ml/min for 40 min andthe mixture was mulled another 30 min. The mixture was transferred to aNauta mixer. The NaKX2.0BD beads of 15% binder was made by following theprocedure of Example #13.

EXAMPLE #15

NaKX(2.0)/12% Binder

2640 gm dry weight of NaKX2.0 (wet weight 4190 gm) and 360 gm dry weightof the ECCA Tex-611 (wet weight 426 gm) were mulled in a muller andwater was pumped in 10 ml/min for 15 min.; then 4 ml/min for 40 min andthe mixture was mulled another 20 min. The mixture was transferred to aNauta mixer. The NaKX2.0BD beads of 12% binder were made by followingthe procedure of Example #13.

EXAMPLE #16

NaKX(2.0)/20% Binder/6% Fiber

2500 gm dry weight of NaKX2.0 (wet weight 3968 gm) and 625 gm dry weightof the ECCA Tex-611 (wet weight 734.7 gm) and 187.5 gm dry weight ⅛″,5.5 Denier RAYON fiber (260 gm wet weight supplied by Mini Fiber Corp)were mulled in a muller and water was pumped in at a rate of 10 ml/minfor 20 min.; then 1.5 ml/min for 100 min. The mixture was then mulledanother 25 min. The mixture was transferred to a Nauta mixer. TheNaKX2.0BD beads of 20% binder and 6% fiber burn-out were made byfollowing the procedure of Example #13. The time spent in the Nautamixer was about 2 hours.

EXAMPLE #17

NaKX(2.0)/15% Binder/6% Fiber

2500 gm dry weight of NaKX2.0 (wet weight 3968 gm) and 441.4 gm dryweight of the ECCA Tex-611 (wet weight 525.7 gm) and 176.5 gm dry weight⅛″ 1.5 Denier RAYON (193.3 gm wet weight) were mulled in a muller andwater was pumped in at a rate of 10 ml/min for 15 min.; then 4 ml/minfor 45 min and the mixture was mulled another 20 min. The mixture wastransferred to a Nauta mixer. The NaKX2.0BD beads of 15% binder and 6%fiber burn-out were made by following the procedure of Example #13. Thetime spent in the Nauta mixer was about 2 hours and 10 minutes.

EXAMPLE #18

NaKX(2.0)/12% Binder/696 Fiber

2640 gm dry weight of NaKX2.0 (wet weight 4190 gm) and 360 gm dry weightof the ECCA Tex-611 (wet weight 429.1 gm) and 180 gm dry weight ⅛″ 1.5Denier rayon (197.2 gm wet weight) were mulled in a muller and water waspumped in at a rate of 10 ml/min for 15 min. then 4 ml/min for 45 min.The mixture was then mulled another 25 min. The mixture was transferredto a Nauta mixer. The NaKX2.DBD beads of 12% binder and 6% fiberburn-out were made by following the procedure of Example #13. The timespent in the Nauta mixer was about 3.5 hours.

EXAMPLE #19

NaKX (2.0)/12% Binder/7% Corn Starch

2640 gm dry weight of NaKX2.0 (wet weight 4190 gm) and 360 gm dry weightof the ECCA Tex-611 (wet weight 429.1 gm) and 210 gm corn starch weremulled in a muller and water was pumped in 10 ml/min for 15 min. then 4ml/min for 100 min and the mixture was mulled another 35 min. Themixture was transferred to a Nauta mixer. The NaKX2.0BD beads of 12%binder and 7% corn starch burn-out were made by following the procedureof Example #13. The time spent in the Nauta mixer was about 2 hours.

EXAMPLE #20

Caustic Digestion of NaKX(2.0)/20%

245.3 gm dry weight of NaKX2.0BD calcined beads of size 6×16 with 20%binder was used for caustic digestion. To prepare the digestionsolution, 79 gm of NaOH (1.975 mole) and 55.1 gm (0.98 mole) KOH weredissolved in 1621 gm of water. To the solution, 70 ml of sacrificialNaKX2.0 BD beads were added and stirred at 9° C. for 2 hours. Thesolution was left to settle and 1404 gm supernatant was collected andthe rest of the caustic was discarded. To this supernatant, 324 ml ofwater, 15.8 gm of NaOH and 11 gm of KOH were added to make up for thediscarded caustic. The resulting solution was used as the digestionsolution. The BD beads were loaded into a stainless steel (SS) column of3″ diameter and the solution was recycled through the column at a flowrate of 45 ml/min at 88° C. for 26 hours. Then 20 liters 88° C., pH 12NaOH solution was pumped through the column to wash the beads. Afterthat, the beads were further washed with 20 liter of pH 8.5 NaOHsolution. The product is NaKX2.0CD. It was air dried and screened tofractions of different particle sizes.

EXAMPLE #21

Caustic Digestion of NaKX(2.0)/15%

327 gm dry weight of calcined NaKX2.0BD beads of size 6×16 with 15%binder 6% 1.5 Denier rayon fiber burn-out was used for causticdigestion. To prepare a digestion solution, 79 gm of NAOH (1.975 mole)and 55.1 gm (0.98 mole) KOH were dissolved in 1621 gm of water To thesolution, 70 ml of sacrificial NaKX2.0BD beads were added and stirred at90° C. for 2 hours. The solution was left to settle and 1404 gmsupernatant was collected. To this supernatant, 324 ml of water, 15.8 gmof NaOH and 11 gm of KOH were added to make up for the discardedcaustic.

The BD beads were loaded into a SS column of 3″ diameter and thesolution was recycled through the column at a flow rate of 45 ml/min. at88° C. for 26 hours. Then 20 liter 88° C., pH 12 NaOH solution waspumped through the column to wash the beads. After that, the beads werefurther washed with 20 liter of pH 8.5 NaOH solution, The product isNaKX2.0CD. It was air dried and screened to fractions of differentparticle sizes.

EXAMPLE #22

Caustic Digestion of NaKX(2.0)/12%

1861.8 gm dry weight of calcined NaKX2.0BD beads of size 6×16 with 12%binder were used for caustic digestion. To prepare a digestion solution,360 gm of NaOH (9 mole) and 251.1 gm (4.475 mole) KOH were dissolved in7386 gm of water. To the solution 320 ml of sacrificial NaK2.0BD beadswere added and stirred at 90° C. for 2 hours. The solution was left tosettle and 6397.7 gm supernatant was collected. To this supernatant,1477.2 ml of water, 72.0 gm of NaOH and 50.2 gm of KOH were added tomake up for the discarded caustic, The resulting solution was used asthe digestion solution.

The BD beads were loaded into two SS columns of 3″ diameter and thesolution from a common reservoir was recycled through each column at aflow rate of 30 ml/min. at 88° C. for 26 hours. After digestion, 40liters of the 88° C., pH 12 NaOH solution was pumped through each columnto wash the beads. After that, the beads in each column were washed with30 liter of pH 8.5 NaOH solution at 88° C. The product is NaKX2.0CD. Itwas air dried and screened to fractions of different particle sizes.

EXAMPLE #23

Caustic Digestion of NaKX(2.0)/12%/Fiber

2400 gm dry weight of calcined NaKX2.0BD beads of size 6×16 with 12%binder 6% 1.5 Denier RAYON fiber burn-out was used for causticdigestion. To prepare a digestion solution, 463.9 gm of NaOH (11.6 mole)and 323.5 gm (5.77 mole) KOH were dissolved in 9517 gm of water. To thesolution 410 ml of sacrificial NaKX2.0 BD beads were added and stirredat 90° C. for 2 hours. The solution was left to settle and 8243.5 gmsupernatant was collected. To this supernatant, 1903.4 ml of water, 92.8gm of NaOH and 64.7 gm of KOH were added to make up for the discardedcaustic. The resulting solution was used as a digestion solution.

The BP beads were loaded into two SS columns of 3″ diameter and thesolution from a common reservoir was recycle through each columnseparately at a flow rate of 45 ml/min. at 88° C. for 26 hours. Then 25liter 88° C., pH 12 NaOH solution was pumped through each column to washthe beads. After that, the beads in each column were washed with 20liter of pH 8.5 NaOH solution. The product is NaKX2.0CD. It was airdried and screened to fractions of different particle sizes.

EXAMPLE #24

Caustic Digestion of NaKX(2.0)/15%/Fiber using NaOH only

327 gm dry weight of 6×16 NaKX2.0BD calcined beads formed with 15%binder 6% 1.5 Denier rayon fiber burn-out was used for causticdigestion.

To prepare a digestion solution, 118.3 gm of NaOH (2.96 mole) wasdissolved in 1621 gm of water. To the solution 70 ml of sacrificialNaKX2.0 BD beads were added and stirred at 90° C. for 2 hours. Thesolution was left to settle and 1392 gm supernatant was collected. Tothis supernatant, 324 ml of water and 23.7 gm of NaOH were added to makeup for the discarded caustic. The resulting solution was used as thedigestion solution.

The BD beads were loaded into a SS column of 3″ diameter and thesolution was recycled through the column at a flow rate of 45 ml/min at88° C. for 26 hours. Then 20 liter 88° C., pH 12 NaOH solution waspumped through the column to wash the beads. After that, the beads werewashed with 20 liter of pH 8.5 NaOH solution. The product is NaKX2.0CD.It was air dried and screened to fractions of different particle sizes.

EXAMPLE #25

Caustic Digestion of NaKX(2.0)/30%/5% Fiber

163.5 gm dry weight of NaKX2.0BD calcined beads of size 8×12 with 30%binder 5% 2.5 Denier rayon fiber burn-out was used for causticdigestion.

To prepare a digestion solution, 79 gm of NaOH (1.975 mole) and 55.1 gm(0.98 mole) KOH were dissolved in 1621 gm of water. To this solution 70ml of sacrificial NaKX2.0 BD beads were added and stirred at 90° C. for2 hours. The solution was left to settle and 1404 gm clear supernantantwas collected. To this supernantant, 324 ml of water, 15.8 gm of NaOHand 11 gm of KOH was added to make up for the discarded caustic. Theresulting solution was used as the digestion solution. The BD beads wereloaded into a SS column of 3″ diameter and the solution was recycledthrough the column at a flow rate of 45 ml/min. at 88° C. for 27 hours.The 17 liters 88° C., pH 12 NaOH solution was pumped through the columnto wash the beads. After that, the beads were washed with 17 liter of pH9.5 NaOH solution. The product is NaKX2.0CD. It was air dried andscreened to fractions of different particle sizes.

EXAMPLE #26

Lithium Ion Exchange

This process is applicable to all of the synthesis examples in theapplication.

694.5 gm dry weight of NaKX2.0CD 8×12 beads were loaded into a glasscolumn of 3″ i.d. A 10″ layer of 3 mm Pyrex glass beads was loaded intothe bottom of the column to serve as a preheating zone for the solution.The column was heated by heating tape wrapped around the column. The ionexchange solution was first passed through a 15 liter 90° C. preheatingflask to partially remove the dissolved air to prevent air bubbles fromforming and being trapped in the column, then the hot solution waspumped into the bottom of the column.

The ion exchange solution was prepared by dissolving 2162 gm LiCl in 80liter distilled water (0.64M); then LiOH solution was added to adjust pHof solution to 9. The solution was pumped through the column at a speedof 15 ml/min. (typically we use 10 to 12 times the stochiometric amountof LiCl). After the ion exchange is completed, the product was washedwith 30 liter of 90° C. distilled water of pH 9 by adding LiOH, withflow rate of 60 ml/min. The washed product was air dried.

EXAMPLE #27

Chemical Analysis and Nitrogen, Oxygen Adsorption Isotherms of LiX2.0CD

Table 9 compares chemical analysis results of a Li X2.0 powder sampleprepared from NaKX(2.0) powder obtained from UOP and sample 16CD. Bothsamples are thoroughly lithium ion exchanged.

TABLE 9 CHEMICAL ANALYSIS OF ADSORBENT SAMPLES Reference 16D LOI wt. %27.56 27.65 Al dry basis 21.88 20.73 Si dry basis 21.95 22.24 Li drybasis 5.25 5.57 Na dry basis 0.06 0.18 K dry basis 0.14 0.12

Table 10 compares nitrogen and oxygen adsorption isotherms of these twosamples The powder sample is of very high crystallinity. The isothermsof two samples are practically identical.

Gas O2 at 20.2 C Gas N2 at 20.2 C Gas O2 at 20.2 C Gas N2 at 20.2 CSample LiX 2.0 pdr Sample LiX 2.0 pdr Sample 16D Sample 16D PressureWeight Pressure Weight Pressure Weight Pressure Weight torr % torr %torr % torr % 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.94 0.02 0.920.11 0.91 0.02 0.85 0.11 20.69 0.04 20.74 0.34 20.55 0.04 20.87 0.3450.74 0.07 50.58 0.65 50.36 0.07 50.32 0.64 104.22 0.12 103.94 1.14104.63 0.13 103.91 1.13 253.01 0.27 252.66 2.19 254.50 0.28 254.27 2.18502.47 0.51 501.18 3.41 502.96 0.52 501.96 3.38 761.26 0.76 758.47 4.29762.04 0.76 760.99 4.26 997.96 0.98 996.84 4.91 998.07 0.98 1003.40 4.891495.70 1.42 1498.00 5.88 1503.65 1.44 1496.75 5.83 1997.85 1.85 1997.106.58 2003.65 1.87 2000.50 6.54 2499.60 2.26 2499.45 7.12 2500.15 2.282502.70 7.10 2997.10 2.67 3002.90 7.57 2999.00 2.68 3002.25 7.55 3477.703.04 3498.75 7.94 3495.20 3.07 3496.45 7.93

The data from these tables suggests that substantially all of the binderused in the sample was converted to zeolite.

EXAMPLE 28

Bonding with Latex-additive

720 gm water, 117 gm dry weight of Kaolin clay (EPK) and 201 gm UCAR 163s latex (solid contained 58.2%) were stirred in a beaker for 15 minutes.This slurry together with 1833 gm dry weight NaKX2.0 zeolite powder (wetweight 2451.7 gm) was mulled for 1.5 hours. The mixture was transferredto a Nauta mixer and mixed for 4.5 hours with 4 oz water sprayed. Itproduced beads with 6% clay with majority of beads in the size range of8×16 mesh. The beads were calcined in a Blue M oven. The temperature ofoven was raised to 600° C. in two hours and kept at 600° C. for 2 hours.The product beads had good physical strength.

The methods of the invention are also applicable to any type ofequilibrium-selective adsorbent material including, but not limited to,X-zeolite, A-zeolite, Y-zeolite, chabazite, mordenite, clinoptiloliteand various ion exchanged forms of these, as well as silica-alumina,alumina, silica, titanium silicates and mixtures thereof. The methods ofthis invention are also applicable to adsorbents used in processes wherethe mass transfer resistance has an effect on performance.

Type X zeolite adsorbents are suggested for air separation, mostpreferably highly-exchanged LiX as described by Chao (U.S. Pat. No.4,859,217). Other type X materials with monovalent cations or mixedcations are also applicable to the present invention such as thosesuggested by Chao (U.S. Pat. No. 5,174,979). In particular, the mostpreferred zeolite is X type with silica to alumina ratio of 2.0 to 2.5and Li cation exchange greater than 70%.

As indicated above, the methods of the invention are also useful forwhen using zeolites having different morphologies. Thus, while one wouldexpect that zeolite powders obtained from different suppliers would havedifferent morphologies given variations in manufacture, the masstransfer rate of adsorbents made from such powders would still beenhanced using the methods of the invention.

The enhanced-rate adsorbents described here are not limited to use inany particular adsorber configuration and can be effectively applied toaxial flow, radial flow, lateral flow, etc. adsorbers. The adsorbent maybe constrained or unconstrained within the adsorber vessel.

The benefits of the invention may also be obtained in PSA processes inwhich the primary product is the more selectively adsorbed component(e.g N₂) or in cycles wherein both the more and less strongly heldcomponents are recovered as product. The adsorbents of this inventionmay also be used in processes such as those disclosed in commonlyassigned applications U.S. Ser. No. 09/622,961 (Ackley et al), U.S. Ser.No. 09/622,889 (Ackley et al) and U.S. Ser. No. 09/622,867 (Mullhaupt etal), the contents of each of which are herein incorporated by reference.

Specific features of the invention are shown in one or more of thedrawings for convenience only, as such feature may be combined withother features in accordance with the invention. Alternative embodimentswill be recognized by those skilled in the art and are intended to beincluded within the scope of the claims.

What is claimed is:
 1. A process for the separation of at least one first component from a gas mixture including said first component and a second less selectively adsorbable component, comprising: contacting said gas mixture in an adsorption zone with a zeolite adsorbent that is equilibrium selective for said first component over said second less selectively adsorbable component and adsorbing said first component on said adsorbent, wherein said adsorbent has an SCRR greater than 1.2.
 2. The process of claim 1, wherein said adsorbent has a median macropore diameter that is greater than 0.1 microns as determined via mercury porosimetry.
 3. The process of claim 1, wherein said adsorbent has a porosity greater than 23%.
 4. The process of claim 3, wherein said adsorbent has a maximum porosity of less than 40%.
 5. The process of claim 1, wherein said adsorbent has a bimodal macropore structure.
 6. The process of claim 5, wherein a first mode of said bimodal macropore structure has a median pore diameter of greater than 2 microns, and a second mode of said bimodal macropore structure has a median pore diameter of greater than 0.1 microns.
 7. The process of claim 1, wherein said first component is nitrogen.
 8. The process of claim 1, wherein said second component is oxygen.
 9. The process of claim 1, wherein said gas mixture is air.
 10. An adsorbent having an SCRR of greater than 1.2.
 11. The adsorbent of claim 10, wherein said adsorbent has a median macropore diameter that is greater than 0.1 microns as determined via mercury porosimetry.
 12. The adsorbent of claim 11, wherein said adsorbent has a porosity greater than 23%.
 13. The adsorbent of claim 11, wherein said adsorbent has a maximum porosity of less than 40%.
 14. The adsorbent of claim 11, wherein said adsorbent has a bimodal macropore structure.
 15. The adsorbent of claim 14, wherein a first mode of said bimodal macropore structure has a median pore diameter of greater than 2 microns, and a second mode of said bimodal macropore structure has a median pore diameter of greater than 0.1 microns.
 16. The adsorbent of claim 11, wherein said adsorbent is substantially binderless.
 17. A process of making an adsorbent comprising the following steps: a) providing zeolite powder having a predetermined composition; b) mixing said powder with a binder capable of being converted to zeolite via caustic digestion, wherein said binder is in an amount less than 20% by weight of the binder/zeolite mixture; c) forming beads from said mixture; d) calcining said beads; e) caustically digesting said beads such that at least a portion of said binder is converted to zeolite; f) recovering said adsorbent.
 18. The process of claim 17, wherein said binder is in an amount less or equal to 15% by weight.
 19. The process of claim 17, wherein said binder is in an amount less or equal to 12% by weight.
 20. The process of claim 17, wherein said process further comprises the steps of: g) adding a combustible fiber or particulate material to said binder/zeolite mixture prior to bead formation to form a binder/zeolite/fiber mixture or binder/zeolite/particulate mixture.
 21. The process of claim 20, wherein said fiber is selected from the group consisting of NYLON, RAYON and SISAL.
 22. The process of claim 20, wherein said fibers are between {fraction (1/32)}″ and ¼″ in length.
 23. The process of claim 20, wherein said particulate material is corn starch or latex.
 24. The process of claim 20, wherein said combustible fiber is added in an amount of 1% to 15% by weight of the binder/zeolite/fiber mixture.
 25. The process of claim 20, wherein said portion of said binder converted to zeolite is at least 50%.
 26. The process of claim 20, wherein said portion of said binder converted to zeolite is at least 80%.
 27. The process of claim 20, wherein substantially all of said binder is converted to zeolite.
 28. The process of claim 17, wherein said predetermined composition includes an exchangeable cation therein.
 29. The process of claim 28, wherein said process further includes the step of ion exchanging said exchangeable cation with lithium following step (e) and prior to recovering said adsorbent.
 30. The process of claim 17, wherein said predetermined composition is NaKX having a SiO₂/Al₂O₃ ratio of less than
 3. 31. The process of claim 30, wherein said portion of said binder converted to zeolite is at least 10%.
 32. The process of claim 17, wherein said predetermined composition is NaKX having a SiO₂/Al₂O₃ ratio of less than 2.5.
 33. The process of claim 17, wherein said predetermined composition is NaKX SiO₂/Al₂O₃ ratio of 2.0.
 34. The process of claim 17, wherein said adsorbent has an SCRR ratio of greater than 1.2.
 35. The process of claim 17, wherein said adsorbent has a median macropore diameter that is greater than 0.1 microns as determined via mercury porosimetry.
 36. The process of claim 17, wherein said adsorbent has a porosity greater than 23%.
 37. The process of claim 36, wherein said adsorbent has a maximum porosity of less than 40%.
 38. The process of claim 17, wherein said adsorbent has a bimodal macropore structure.
 39. The process of claim 38, wherein a first mode of said bimodal macropore structure has a median pore diameter of greater than 2 microns, and a second mode of said bimodal macropore structure has a median pore diameter of greater than 0.1 microns. 